Method of bleaching paper-pulp, &amp;c.



No. 702,|42. Patented lune lo, :902.

F. H. Loma.

I METHOD 0F BLEAVACHING PAPER PULP, GLC.

(Application filed June 24, 1901.)

i UNITED STATES PATENT OFFICE.

FREDERIC H. LONG, OF CHICAGO, ILLINOIS,ASSIGNOR TO THE MYSTIC REDUCTIONCOMPANY, 'A CORPORATION V'METHOD oF BLEACHING PAPER-PULP, sbc.

SPECIFICATION formingpart of Letters Patent No. 702,142, datedil une 10,1902. Application filed June 24, 1901. BeriaIND. 65 ,742.c (Nospecimens.)

Be it known thatl, FREDERIC H. LONG, a resident of Chicago, Cook county,Illinois, have invented certain new and useful Improvements in Methodsof Bleaching Paperv Pulp and the Like, of which the. following isdeclared to be a full, clear, and exact description. Y

The invention aims to provide an efficient and economicalelectrochemical process for bleaching paper-pulp and the llike, and inparticular chemically or mechanically prepare wood-pulp from which paperis t'o be In most prior electrochemical processes forv bleaching achlorid solution is electrolyzed in one tank and then run into thebleachingtank containing the paper-pulp or other material to be actedupon. In such methods much of the noxiousjchlorin gas escapes and iswasted. The bleaching agent is inefficiently applied and theelectrolyzing tanks or cells quickly become polarized. By my improvedmethod the paper-pulp or the like is mixed with the salt solution andthe mixture or charge is directly subjected to an electrolyzing-currentin a closed tank or vessel under pressure, while the charge ismaintained in circulation between the anode and ,cathode elements. Inthis manner the nascent chlorin and other bleaching agents formed actvery efficiently and direct'upon all `parts of the pulp or othermaterial and there is no danger of escape and waste of the evolvedchlorin.

Preferably, also, the cathode products formed are constantly separatedfrom the body of the charge and are removed from the cell to avoidpolarization and to prevent a reduction in the amount of effectivebleaching agent by the chemical reunion of the electrolytic products.

.tervals in' its outer rim.

The electrolytic vessel or cell lA receives the paper-pulp to bebleached diluted with a solution of common salt, (sodium chlorid.) Otherchloride may be used-as, for example, magnesium chlorid. The saltsolution is preferably of a density of 12J to 18o Baume and is added insufcientvolume to render the charge of the consistency of thick cream. Asmall 'amount of quicklime is preferably supplied in the proportion offive toten pounds to each four thousand pounds of salt solution in orderto insure alkalinity of the charge'during electrolyzation'and for otherpurposes, as

hereinafter indicated.,4

metal tank-body 10, which is provided with va valved inlet-pipe` 11,through which the charge is admitted to the desired level, as shown bythe gage-glass 12. The cup-shaped bottom 13 is provided'y with a woodenlining 14'which` supports a shallow copper pan 15,

constitutingthe cathode element of the cell.

The panishin metallic connection with a depending circular series ofcopper rods 16,

atw their outer ends to a copper ring 17, having a wire. terminal 18connected therewith.

.lous paper, which serve to exclude the solid,

iwhile the liquid portionsof the charge may pass through. Supported upona ring 21 and held in place thereon by blocks 22, intermediate theendsof the vessel, is l`aV conical partit-ion or spreader 23, havingnotches-24: at in- The anodes'consist of hard-carbon pole-heads 25,arranged in circular series beneath the'partition 23 and each united bya long copper rod 26, extending upwardly through the top of the cell toa copper ring 27, which is connected bya wire 28 With the source of theelectricity." The rods 26 are insulated from the top .by suitablesleeves 29.

The charge is maintained in forced circulation tok thoroughly agitatethe mass to aid the chemical'action of the bleaching element to keep thesurface of the diaphragm or pad free extending through the bottom 13 anduniting l ICO the charge to iiow along between the anodes and thediaphragm, so as to successively expose all parts of the charge to thedisruptive inuence of the electric current. This circulation ispreferablyeifected by means of an ejector 30, the inlet-port of which isconnected to a bent pipe 3l, projecting through the bottom of the vesseland extending above the diaphragm. The outlet-port of the ejector isconnected by a valved return-pipe with the top of vthe vessel, whichpipe connects for convenience with the inlet or feed pipe 11. Compressedair or steam under pressure is supplied to the ejectornozzle 33, and bythis means the cell contents are constantly withdrawn from the bottomand returned into the top, from which they How over the partition orspreader 23 through notches 24 and between the anodes 25 and thediaphragm. A ventpipe 34, preferably leading outside of the building andprovided with a shut-off cock and regulatingvalve serves to relieve anyexcessive pressure of gases or vapors evolved during the process. Inthis way all portions of the charge are exposed to the disruptiveinfluence of the electric current, the chlorid is decomposed, and thebleaching agents are directly applied in a nascent condition to allportions of the pulp, the bleaching of which thus proceeds rapidly andeiiiciently. By carrying on the processin a confined space underpressure the efficiency is considerably increased, the bleaching agentsformed are more readily maintained in solution in intimate contact withthe pulp, all danger of a wasteful escape of noxious gases isavoided,and the cell rendered less liable to polarization. An excess offree chlorin presentin thecharge wouldhaveadeleteriouseffect upon thestrength of the fiber; but the lime present not only insures thealkalinity of the charge, but prevents the presence of an excess of freechlorin, which, together with the released anions, is effective for thedecomposition of the resinous and other coloring-matters of thepaper-pulp. The cathode products, together with the decomposedcoloring-matters in solution, are continuously isolated from the chargebeneath the diaphragm and prevented from reuniting with the bleachingelements. The liquid cathode products thus formed and separated aredrawn olf periodically or continuously, if desired, through the petcock37, opening into the vessel beneath the diaphragm. The gases and vaporsevolved by the chemical and caloritic eifects at the cathode elementunless removed will accumulate and be entrapped beneath the diaphragm ofcotton duck and bibulous paper and would increase materially theresistance to the passage of the current between the cathode and anodethrough the electrolyte, and so interfere with the electrolytic action.Means are therefore provided for removing the gaseous cathode products,and for this purpose a pipe 38 is preferably employed, which pipeconnects with the space beneath the diaphragm and extends upwardly abovethe level of the solution contained in that space. This pipe ispreferably connected to the vent-pipe 34, intermediate the valves 35 and36, as indicated in the drawings. I also preferably bend the lower endof the pipe in the form of a Ushaped portion the end of which grojectsto some extent through the bottom of the vessel and affords a suitablelocation for a gage-glass 0 and a thermometer 42, by which the conditionof the solution below the diaphragm may be noted andthe electric currentregulated accordingly. This U-shaped portion will not act as a trap toprevent the escape of the gas or vapor, since the liquid beneath thediaphragm is in a state of violent ebullition and the gas 0r vapor isdeveloped under sufficient pressure to overcome the short hydrostaticcolumn in this U- shaped portion 39 and is removed practically as soonas found. The long upwardly-extending pipe 38 acts as a separator toprevent any of the liquid from being entrained and carried off by theescaping gas; but a valved branch pipe 39 is provided, leading to asuitable receptacle and will serve to collect any small portion ofliquid so forced up into the pipe. By this means the liquid and gaseouscathode products, consisting, chiefly, of sodium hydroxid and hydrogengas, together with the decomposed coloring-matters in solution, areeffectively isolated from the charge and removed from the cell. Thisforms an important feature of my invention, since the removal of the gasdiminishes the resistance of the cell and its liability to becomepolarized, and the separation and removal of the sodium hydroxidprevents it from diffusing upwardly through the charge and weakening theeffect of the bleaching agents by combining chemically therewith. So,also, the separation and removal of the decomposed coloring-matters insolution aids inateriallyin obtaining a well-bleached product, whichwith previous electrochemical processes is often discolored and full ofblack specks.

It is obvious that changes may be made in the details of the'improvedprocess without.

departure from the essentials of the invention and that any suitableform of apparatus may be employed in carrying it into effect. Otherhalogen salts of the alkali and alkaline earths could be employed in theplace of common salt or of magnesium chlorid; but the latter are themost available.

Having thus described my invention, what I claim as new, and desire tosecure by Letters Patent, is-

l. The process of bleaching pulp and the like in a closed vessel, whichprocess consists in subjecting a mixed charge of pulp and dilute chloridsolution to an electrolyzing-current and,while confined underpressure,main taining the whole charge bodily in circnla tion betweenthe anode and cathode elements, substantially as described.

2. The process of bleaching pulp and the IOO IIO

like in a closed vessel, which process consists in subjecting a miXedcharge of pulp and dilute chlorid solution to an electrolyzing-'current,simultaneously isolating the gaseous and other refuse cathode productsfrom the' body'of the charge and, While confined under pressure,maintaining the Whole chargeV bodily in circulation between the anodeand cathode elements, substantially as described.

3. The process of bleaching pulp and the like in a closed vessel, whichprocess consists in subjecting.,r a mixed charge of pulp and dilutechlorid solution to an electrolyzing-current, expelling the gaseous andother refuse cathode products and, While confined underpressnre,maintaining the Whole charge bodily in forcedcirculationbetween the anode and cathode elements, substantially asdescribed.

4. The'process of bleaching paper-pulp and the likein a closed Vessel,which process con-` sists in subjecting a mixed chargeof pulp and dilutechlorid solution With a neutralizing addition to anelectrolyzing-current, and while. i 1

confined under pressure, maintaining the whole charge bodily in forcedcirculation bestantially as described. I

FREDERIC H. LONG.

Witnesses:

`ALBERTA ADAMIOK, HARRY L. CLAPP.

25 tween the anode an'dcathodeelements, sub-

